Immunoglobulin bound on the surface of bacteria mediates phagocytosis by:
**Core Concept**
The process of phagocytosis is a critical mechanism of the immune system, where cells engulf and digest foreign particles, including bacteria. Immunoglobulins (antibodies) play a crucial role in marking pathogens for destruction by binding to specific antigens on their surface.
**Why the Correct Answer is Right**
The correct answer involves the concept of opsonization, where antibodies bind to antigens on the surface of bacteria, making them more susceptible to phagocytosis. This process is mediated by the Fc receptor on the surface of phagocytic cells, such as neutrophils and macrophages. When antibodies bind to the Fc region of the immunoglobulin, they activate the Fc receptor, which in turn triggers the engulfment and destruction of the bacteria.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the mechanism of phagocytosis mediated by immunoglobulins. While complement proteins can also mark bacteria for destruction, the primary mechanism in this context is opsonization by antibodies.
**Option B:** This option is incorrect because it is too vague and does not specifically describe the role of immunoglobulins in mediating phagocytosis.
**Option C:** This option is incorrect because it is unrelated to the concept of phagocytosis and the role of immunoglobulins in mediating it.
**Clinical Pearl / High-Yield Fact**
The ability of antibodies to opsonize bacteria is a key mechanism by which the immune system protects against infection. This process is often enhanced by the presence of complement proteins, which can also mark bacteria for destruction.
**Correct Answer: C. Complement proteins.